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Ships and Shipbuilding: Design and Construction
indicate pages available in the manuscript viewer]When we think about design today, we think in terms of measured drawings prepared in an office. We use these drawings to determine the exact shape of whatever it is we are making—before we start building. We use drawings to store good designs so we can make them again when we need to.
Neither measured plans nor even the technique for making them existed in the Middle Ages. Ship design, in the sense of determining final dimensions, was carried out in the yard at the same time as a ship was actually made. The main difficulty was not one of determining overall shape, but of determining the dimensions of hundreds if not thousands of individual parts that had to be cut from timber and assembled together. Some other way of storing good designs and retrieving them for later use had to be used.
Michael's treatise on shipbuilding reflects two approaches to these problems. For the types of ships built in private shipyards, he describes a system based on a proportional approach; for the galleys built in the state-run Arsenal, his approach reflects the recording of actual measurements on paper.
Proportional approach
Describing his nave latina, Michael quickly gives a series of dimensions for parts of the hull (164b). First he gives the length of the keel. Next he gives measurements for the midship frame, including the piano, trepie, bocha, and the height of the deck. Then he gives the overall length of the ship on the deck.
The midship frame was the frame located at the widest part of the hull. All the frames forward from the midship frame narrowed toward the bow. All the frames aft of it narrowed toward the stern. "Piano" means floor; this measurement defined the flat bottom of the hull from the keel out to the "turn of the bilge," where the frame timbers turned up to form the side of the vessel. The trepie was the breadth of the frame at a point three feet above the ground. The bocha was the width of the frame at its maximum breadth, measured at the height of the deck.
Michael's text does not include any other dimensions for the nave latina or nave quadra. This reflects a basic feature of commercial ship design in the Middle Ages. The shape of a ship was fundamentally defined by the length of its keel, the length of its deck, and the shape of its midship frame.
Here is how Michael's text arrives at the basic dimensions of the nave latina:
We wish to make a lateen ship whose keel is 12 paces long. We want the floor to be as many feet as the keel is long in paces, and one-quarter less. This will be 9 feet.
And this ship with a keel of 12 paces and a floor of 9 feet should have for its trepie as many feet as the keel is long in paces and one-third more. The keel is 12, a third more would be 4, making 16 in all.
And this ship with a keel of 12 paces and a floor of 9 feet and a trepie of 16 feet needs a breadth equal to the trepie, and half again. That is 24.
And this ship with a keel of 12 paces and 9 feet in the floor, and a trepie of 16 feet, and a breadth of 24 feet, should have a deck height of as much as the floor and a half-foot more, that is 9 1/2 feet.
And this ship with a keel of 12 paces and 9 feet in the floor, and a trepie of 16 feet, and a breadth of 24 feet, and a rise of 9 1/2 feet, should have deck length equal to the keel and one-quarter more. It will be 15 paces.
What we see here is that the principal dimensions of the vessel are all derived from the length of the keel by following a series of proportional rules, or at least by a series of rules involving fractions that were easy to remember. Most later texts add a few more rules for the dimensions of the stemposts and sternposts. Michael's description of the nave latina and the nave quadra leaves these out because the real focus was on the sails and rigging.
The dimensions given in the text are not for the length and breadth in the abstract. They are given for actual, big, thick wooden timbers. This reflects a second fundamental feature of ship design and construction in Michael's day. Since it was not possible to remember rules defining the hundreds and thousands of parts of a hull, the idea was to erect the principal parts of the hull in the yard, then derive the dimension of other parts from the structure itself as it slowly took shape.
This is how the design of vessels like the nave latina and the nave quadra were completed in the Middle Ages. The basic dimensions of a standard design were stored in the minds of shipbuilders in the form of a series of rules involving fractions (if not proportions) that could be easily remembered. To "design" a new ship of a standard type, the master shipwright only needed the length of the keel. From the length of the keel, he could quickly derive the other principal dimensions, then lay the keel, set up the midship frame, raise the stem and stern, then set to work deriving the rest of his measurements the ship itself.
Paper approach
If most ships in the Middle Ages were designed according to a set of proportional or fractional rules, the most noticeable thing about Michael's description of galleys is that the proportions are missing. In their place is a long list of actual measurements for different parts of the hull that generally follow the sequence of construction.
The list reveals two important things. The first is that Michael's text is not about the design of a galley from scratch. It is about the construction of a standard ship that has already been designed. Over the years, scholars have done an excellent job reconstructing the original design techniques. Michael's text does not attempt to describe these methods.
The second point to stress is that such a list represents a very different method of storing designs when compared to the proportional rules used for sailing ships. Those rules could easily be remembered by a shipwright. It was not possible for any shipwright to remember the dozens and dozens of measurements listed in Michael's text. That is to say, they could not be stored in the mind; they could only be stored on paper.
This radically different approach to the storage of designs reflects the context in which the galleys were constructed. They were all built by the Venetian government in its own shipyard, known as the Arsenal. They were extremely expensive to build. They were built with the public's money. They often had to be built quickly, frequently several at a time. Naturally, given the cost, state officials wanted to know what they were building and make sure they were building the best ships for the money. In short, the context for this different approach to design storage was decidedly bureaucratic.
But even if the principal dimensions were stored differently, galley builders shared many ideas with their sailing-ship brethren. Perhaps the most fundamental is that the design of the galley came to be completed in the dockyard using the structure itself. Accordingly, Michael's list of measurements comes in distinct sections corresponding to the sequence of construction. We can learn more about galley design and construction by following this sequence:
Keel
The first step in construction was to lay the keel on a series of posts driven into the ground. The keel of a galley was a long, thick timber that provided the foundation for the entire ship's structure. The keels of galleys were slightly curved. This curve was determined using a long, suspended rope. The height of the posts was adjusted accordingly and the keel timber laid on top.
Stem and sternposts
The next step was to raise the stem and sternposts. These were two thick timbers defining the curve of the bow and stern. They were scarfed, or joined, to either end of the keel. Michael called each scarf the poselexe del choltro ( 139b).
Midship frame
Each galley had four or five identical frames located midway between stem and stern. Michael referred to them as the chorbe de mezzo. These "midship frames" defined the shape of the hull at its maximum breadth. Michael does not discuss how the curve of these frames was determined. Instead, he lists a series of measurements describing the breadth of the frame at successive heights above the keel. One of the most important dimensions was that of the piano, or floor, which was the width of the flat bottom part of the hull from the keel out to the "turn of the bilge" where the frame curves up to form the ship's side. Another most important measurement was the bocha—literally "mouth"—which was the maximum breadth of the frame at the height of the deck. The third important measurement was, of course, the height of the deck itself. Michael gives a diagram of the midship frame ( 140b).
Tailframes
In the galley of Flanders, there were 42 frames forward and 42 frames aft of the four midship frames. The floors and maximum breadth of each of these frames gradually narrowed and rose from stem to stern, defining the long, graceful curve, or sheer, of a galley's side. Michael does not describe any method for determining this sheer. It was known, however, that the lines governing the changing shape of the frames could not be extended all the way to the ends of the ship, because they didn't give the right shape to the bow and stern. Frames that were governed by the lines were called chorbe in sesto, or "moulded" frames. The last of these moulded frames were called the chodiera chorbe. These "tailframes" were erected at each end of the ship after the midship frames had been set up. Michael gives their basic dimensions.
Additional frames
Michael does not say so directly, but his text suggests that two additional frames were set up at this point. One was located 18 feet forward of the midship frames, the other 18 feet aft.
Wales
The next step was to attach the wales, which were extremely thick timbers stretching from stem to stern along the outside of the frames. The wales fastened the frames in place and thus gave the hull structure greater longitudinal strength. Michael gives measurements for the height of the wale at the midship frame, at the 18-foot frame further back, at the 18-foot frame further forward, and at the tailframes.
Madier di bocha
For each of the frames erected so far, Michael gives a measurement from the wale to a longitudinal timber called the madier di bocha. It is difficult to find an exact English equivalent for this timber. It was not as thick as a wale, but it extended along the top of all the frames from stem to stern at the height of the deck and helped clamp the frames in place.
Ribbands
Ribbands were long, thin, wooden laths or battens. They were bent around the frames and stretched all the way from the bow to the stern. Michael describes the positioning of three ribbands, one above the other, and gives measurements for their location at the midship frame, the 18-foot frames, and the tailframes. The curves of the ribbands defined the shape of the hull. The key dimensions of all the other moulded frames could be determined using the ribbands, as well as the madier de bocha and the wales.
Bow and stern frames
As noted above in the discussion of the tailframes, the shape given to the bow and stern by bending the ribbands around the frames was incorrect. The next step in construction was therefore to adjust the shape of the bow and stern. This was done by placing an additional frame, or at least a frame template, on top of the keel scarphs midway between the tailframes and the stem and stern at either end. Michael provides diagrams for these frames, detailing how and where the ribbands should curve around them. An additional diagram concerning the longitudinal shape of the bow and stern is included, but he does not explain its use ( 138b, 139a).
At this point, the shipwright following Michael's steps could determine all the dimensions for all the other frames and timbers by measuring the structure. It's here that Michael's list of measurements ends.